The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Known vehicle systems use hybrid powertrain architectures to generate at least a portion of required tractive torque originating from a non-hydrocarbon-fueled motor, including an electric machine that transforms electric power to mechanical torque. Powertrain architectures may be configured to transfer tractive torque to an output member through a transmission device. Such powertrain architectures can include series-hybrid configurations, parallel-hybrid configurations, and compound-split hybrid configurations. Electric machines operative as both motors and generators can be controlled to generate torque inputs to the transmission independently of a torque input from the internal combustion engine. The electric machines may react and transform vehicle kinetic energy transmitted through the vehicle driveline to electrical energy that is storable in an electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain, including controlling transmission operating range state and gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange among the electrical energy storage device and the electric machines to manage torque and rotational speed outputs of the transmission.
Known electrical circuits for providing electric power to electric machines include a high-voltage DC electrical energy storage device that supplies DC electric power via a high-voltage bus through a DC link to an inverter which transforms the DC electric power to AC electric power to power the electric machine. The electric machine is preferably a multiphase synchronous AC machine including a stator and a rotor magnetically coupled to the stator.
Performance of an electric machine, specifically generation of torque for either propulsion or reaction associated with regenerative braking, is constrained by magnitude of the DC voltage at the DC link to the inverter.
The series path power capability to and from the high-voltage DC bus is limited by a magnitude of voltage at the DC link to the inverter, which affects mechanical power output from the electric machine connected thereto. The magnitude of voltage at the DC link to the inverter can be constrained by magnitude of the DC voltage available from the high-voltage DC electrical energy storage device that is transferred to and from the high-voltage DC electrical energy storage device.
A known solution for increasing the magnitude of voltage at the DC link to the inverter includes using a high-voltage DC electrical energy storage device having a greater voltage level than the high-voltage DC electrical energy storage device. Another known method for increasing the magnitude of voltage at the DC link to the inverter includes adding a DC/DC boost converter between the high-voltage DC electrical energy storage device and the DC link to the inverter. Another known method for increasing the magnitude of voltage at the DC link to the inverter includes adding an ultracapacitor bank to the DC link for the inverter. Each of these known solutions utilizes packaging space in the vehicle, adds weight, and increases complexity of the electrical system.